Portable Gas Generating Device

ABSTRACT

Methods and devices for generating gas from nitrous oxide are provided as well as downstream uses for the product gas. Reactor devices of the invention are compact and incorporate a novel heat-exchange/regenerative cooling system to optimize N 2 O decomposition and reactor durability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/537,439, entitled “Portable Gas Generating Device”, filed Sep. 29,2006, which claims priority to U.S. Provisional Application Ser. No.60/786,965, filed Mar. 29, 2006, entitled, “Method and Devices forGenerating Gas from Nitrous Oxide,” and is related to U.S. Pat. No.6,347,627, each of which are incorporated by reference in theirentirety.

This invention was made with Government support under Contract No.W31P4Q-04-C-R322 awarded by the U.S. Army. The U.S. Government may havecertain rights in this invention.

FIELD OF THE INVENTION

The invention generally relates to a gas generating device and inparticular to a portable gas generating device for production of highenergy gas from nitrous oxide and to the uses thereof.

BACKGROUND OF THE INVENTION

Decomposition of nitrous oxide (N₂O) results in the release of oxygen,nitrogen, and a large amount of energy. Over the past several decades,groups have tried to optimize and capture the energy released from thisdecomposition reaction, thereby making it more practical for downstreamuse.

In particular, U.S. Pat. No. 5,137,703 describes a method for thermalcatalytic decomposition of N₂O into molecular oxygen and nitrogen usinga variety of catalysts. U.S. Pat. No. 5,171,553 describes noble metalcatalyst for the decomposition of N₂O that provides increased reactivitywhen used on noble metal-exchanged crystalline zeolites. U.S. Pat. No.5,314,673 describes a method for decomposition of streams of up to 100%N₂O over a tubular reactor filled with cobalt oxide and nickel oxide onzirconia catalyst. Additionally, U.S. Pat. No. 6,347,627 describes aself-contained system for converting N₂O to a breathable gas mixture.

One particularly attractive use for N₂O is as an energy source in apropulsion system, e.g., monopropellant, bipropellant, etc. Liquidmonopropellants are often used in propulsion systems where simplicity ofdesign, restartable control on demand, and repeatability are desired.Conventional monopropellants include hydrazine and hydrogen peroxide,both of which are toxic and extremely dangerous.

There is a need in the art to replace hydrazine and/or hydrogen peroxidewith a safer, but still effective energy source. In addition, there is aneed in the art to more effectively optimize N₂O decomposition,especially in a manner that provides portable, useful energy and highpressure gas, e.g., useful as an engine propellant for a rocket engine,a turbine, etc.

Against this backdrop the present invention has been developed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the density of N₂O as a function oftemperature.

FIG. 2 is a graph showing the vapor pressure of N₂O as a function oftemperature.

FIG. 3 is a cross-sectional view of the N₂O generator in accordance withone embodiment of the present invention.

FIG. 4 is an exploded view of the N₂O generator in accordance with oneembodiment of the present invention.

FIG. 5 shows the flow direction of N₂O through a cross-sectional view ofan embodiment of the generator in accordance with the present invention.

FIG. 6 is a perspective view of the reaction chamber and nozzle inaccordance with one embodiment of the present invention.

FIG. 7 is a cross-sectional view of the N₂O generator in accordance withan alternative embodiment of the present invention.

FIG. 8. shows the flow direction of the N₂O through a cross-sectionalview of an embodiment of the generator in accordance with the presentinvention.

FIG. 9 is a perspective view of the screen and nozzle in accordance withone embodiment of the present invention.

FIG. 10 is a side view of N₂O flow direction through a screen embodimentin accordance with the present invention.

FIG. 11 is a top view of the screen in accordance with one embodiment ofthe present invention.

FIG. 12 shows the flow direction of the N₂O and openings through ascreen of one embodiment in accordance with the present invention.

FIG. 13 illustrates the vapor pressure and density curve for N₂O as afunction of temperature.

FIG. 14 illustrates adiabatic temperature and maximum theoretical Ispperformance from decomposed LN₂O as a function of percent decompositionand initial tank temperature.

FIG. 15 illustrates the sensitivity of N₂O decomposition time as afunction of temperature for the two bounding cases of isothermal andisenthalpic flows.

FIG. 16 illustrates the reaction time for N₂O as a function oftemperature in the presence of various catalysts.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a compact and portable gasgenerator (“generator” herein) for production of high energy gas fromdecomposition of N₂O. Generator embodiments of the invention allow forthe generation and control of large quantities of high energy gas.Generator embodiments are constructed to both raise the efficiency ofN₂O decomposition, thereby increasing the volume of gas and energyreleased, and enhances the durability of the generator itself, therebydecreasing the rate of generator failure. In addition, generator designsof the invention are highly portable; having a size per power outputthat vastly improves on existing power production technology. Finally,generator embodiments of the invention can provide combined uses, forexample in one operational use the generated gas is used for propulsionand in another operational mode the generated gas is used as breathableair.

Particular embodiments of the invention provide a novel heat exchangedesign that facilitates transfer of heat from N₂O decomposition in thegenerator to the incoming N₂O reactants, thereby preheating the N₂O topre-decomposition temperatures and controlling the temperature of thegenerator itself. The heat transfer, therefore, increases the efficiencyof N₂O decomposition, while facilitating the durability of thegenerator, as the enhanced heat release (cooling) acts to protect theintegrity of the metals used to fabricate the generator.

Generator embodiments of the invention are used as monopropellantengines; as part of bipropellant or hybrid engines; as buoyancy enginesfor underwater vehicles; as mono-propellant drivers for turbineemergency power units (EPUs); as sources for breathing gas, for mixeduses, i.e., propellant and breathable air, and for other uses asdescribed below.

N₂O Decomposition

Nitrous oxide, N₂O, is a common and inexpensive storable chemical thatin the present invention is used as a convenient, low cost, lightweight,safe, and reliable source of high energy gas. N₂O is stored as a liquidat atmospheric pressure and about −90° C., or at ambient temperaturesand about 50 bars pressure. The density and vapor pressure of liquid N₂Oas a function of temperature are shown in FIGS. 1 and 2. When heated toa temperature of about 600° C., N₂O will spontaneously decompose to agaseous mixture consisting of one-third oxygen and two-thirds nitrogenby mole. Use of a catalyst decreases the temperature at which thedecomposition reaction occurs. As shown below, a large amount of energyis released during the decomposition reaction.

Nitrous oxide is an energy-bearing molecule, at 298 K, N₂O containsabout 81.6 kJ/mole more enthalpy than molecular oxygen and nitrogen.Thus, based on the energy balance, N₂O is unstable and shouldspontaneously decompose to oxygen and nitrogen, according to reaction 1:

N₂O→N₂+½O₂+81.6 kJ  (Rxn 1)

All that is required for Reaction 1 to proceed in the forward directionis sufficient kinetic activity to allow the decomposition to proceed.This decomposition will occur in the gas phase and almost to completionat about 600° C. (or at lower temperatures when an appropriate catalystis present).

The overall enthalpy of reaction for N₂O is 1855 kJ/kg. Including theheat of vaporization loss of 376 kJ/kg, the resultant available thermalenergy release from liquid (L) N₂O is 1479 kJ/kg (410 Whr/kg). Twentypercent of the decomposition energy of N₂O is required to vaporize theliquid propellant.

As shown in the examples below, N₂O is able to provide specific impulse(Isp) performance comparable to current industry standardmonopropellants, such as hydrazine and hydrogen peroxide. In addition,N₂O is a substantial improvement over a cold compressed gaseous nitrogensystem which is used for propulsion for various reaction controlsystems. As such, the potential energy from N₂O decomposition is equalto the materials currently in use in most monopropellant engines(rocket, turbine, etc.), i.e., comparable or better than hydrazine,hydrogen peroxide and gaseous nitrogen.

It should also be noted that due to nitrous oxide's freezing point(−90.8° C., Baker, 1971) it is highly useful in extreme cold conditions,for instance, deep-space-storage and operation. This is compared tohydrazine and hydrogen peroxide which have freezing points of 2° C. and1° C., respectively. N₂O is also useful when the temperature isextremely warm due to its high thermal stability. As such, N₂O for theseadditional reasons is a superior reactant for generator use underextreme conditions, e.g., space, underwater exploration, thermal pools,etc.

Various catalysts can be included in N₂O decomposition reactions of thepresent invention. Catalysts reduce the temperature required todecompose the N₂O. A suitable catalyst must survive the high temperatureand oxidizing environment of the reaction. Several catalyst have beenidentified herein that show substantial ability to lower the N₂Odecomposition temperature while surviving for a long enough interval tomake economic sense. These catalysts include rhodium, ruthenium,platinum, nickel, zirconia, magnesia and copper. In preferredsituations, the catalyst is coated onto an appropriate substrate, forexample, alumina, zirconium oxide, or magnesium oxide (the substrateacting as a support and to extend the life of the catalyst coating).

Generator Embodiments

Generator embodiments of the present invention are designed to optimizethe release of energy from nitrous oxide decomposition and to maximizethe durability of the generator for sustained and long-term use. Inaddition, generators of the present invention have been optimized tomaximize energy release for size of the device; this facilitates theproduction of cost effective and highly portable generator devices.

In one embodiment, the generator accomplishes these substantial benefitsby providing a highly compact heat-exchange zone within the generatorfor pre-heating the incoming N₂O (making the decomposition reactionsubstantially more efficient) while simultaneously cooling the generatorparts by release of heat from the reaction chamber (protecting thegenerator parts from the extreme temperatures of the N₂O decomposition).

A cross-sectional view of one embodiment of the generator is shown inFIG. 3. The generator 300 includes generally: a reaction chamber 302operatively connected to an exit chamber 304, an exterior jacket 306that envelops the reaction chamber; an injection cone 308 that envelopesthe exit chamber 304; and a cap 310 for operatively connecting theexterior jacket 306 to the reaction chamber. As discussed in more detailbelow, a gap 312 exists in the jacket, the gap including one or morechannels provided between an interior wall 314 and exterior wall 316 ofthe reactor chamber 304. The gap provides a constrained space by whichN₂O flows from the exterior of the generator 318 (source of N₂O) intothe reaction chamber for decomposition and release of gas. The gap 312in the exterior jacket 306 provides a heat exchange area in which N₂O ispreheated during transit from its entry point into the generator 300 towhere it decomposes within the reaction chamber 302.

At one end of the reaction chamber, the cap 310 acts to divert N₂Oflowing within the gap 312 to a release point in the reaction chamber302. At the opposite end of the reaction chamber an exit chamber may beoperatively connected. The exit chamber 304 is enclosed by the injectioncone and is for release of the gas generated within the reaction chamberto the exterior 318 of the reactor. The exit chamber 304 is shownenveloped by the injection cone. Note that an exit chamber is especiallyuseful when the generator is used to produce high energy gas for rocketapplications. The exit chamber, however, is not required in generatoruses that do not require constrained or concentrated release of the highenergy gas. Embodiments shown herein typically include the exit chamber,but note that this feature is optional.

In one embodiment, the generator has an overall cylindrical shape withdimensions from about 1 to about 3 inches (in) in diameter and about 1to about 6 inches in height. Reactor chambers 302 within the generatortypically have volumes of from about ½ to about 12 cubic inches whichtends to provide sufficient gas/energy for most uses. In particular, areactant volume of from about 1 to about 6 cubic inches is envisionedfor use in most “engine” embodiments. Reaction chamber wall 314thickness is also variable, but is typically from about 0.05 to about 1inch in thickness. Other generator size dimensions are envisioned to bewithin the scope of the application as long as the generator functionsas described herein are maintained.

Still referring to FIG. 3, the reaction chamber 302 is sufficient toallow decomposition reactions of N₂O and in some embodiments house asufficient amount of catalyst to allow for the generation of gas andenergy as described herein. A partition 320 is shown positioned betweenthe reaction chamber 302 and the exit chamber 304 to constrain thereactants and catalyst within the reaction chamber. In embodiments wherecatalysts are not included in the reaction chamber, a partition is notalways required.

In one embodiment, the partition 320 can be a screen or other likedevice having a series of openings (see FIG. 8) that fluidly connect thereaction chamber 302 to the exit chamber 304. High energy gas from N₂Odecomposition passes from the reaction chamber into the exit chamber viathe openings within the partition 320. The openings may be in the formof holes, slits, or other like apertures. Typically, partition 320embodiments are fabricated from materials having high thermal stability,i.e., very low to no thermal expansion coefficient. For example,materials like zirconia foam and sodium zirconiam phosphate.

FIG. 4 shows one embodiment of an exploded view of a generator 300embodiment including the reaction chamber inner wall 314, generatorouter wall 322, reactor cap 310, nozzle wall 324 and injection cone 308.The reactor chamber inner wall and exterior wall (inner side ofgenerator outer wall) combine to form jacket 306.

An injection port 326 is located through the injection cone 308connecting the gap formed between the interior and exterior chamberwalls with the exterior of the generator. (See FIG. 3). In oneembodiment, the injection port 326 is located distal to an entry port327 of the reaction chamber 302 to thereby maximize heat-exchangebetween the N₂O flowing within the gap 312 and heat released from thereaction chamber. Also note that the nozzle wall 324 defines aconvergence zone 328 for concentrating the released gas from thechamber, a throat zone 330 for controlling the flow rate of gas from thechamber and a divergence zone 332 for maximizing the exhaust velocity ofthe gas. Optionally, a collar 334 can provide an attachment fordownstream plumbing useful with the present invention.

Referring to FIG. 5, one embodiment of N₂O flow direction is shownwithin the generator 300. N₂O is injected into the generator via one ormore injection ports 326, the fluid flows into a channel 336 formedbetween the injection cone 308 and the nozzle wall 324. N₂O is injectedeither as self pressurized gas or as a liquid. Note that the nozzle wallis typically continuous with the inner reaction chamber wall 314.

In one embodiment, the one or more channels defined within the gap 312are formed substantially the entire length of the jacket 308 formed bythe interior 314 and exterior 316 walls of the reaction chamber. Thechannels can be straight, zigzagged, spiral, non-uniform or the like.Channels can be of various useful dimensions, for example can be formedas cross-sectional U-shapes, circular shapes, square shapes, as well asother like geometries. In addition, it is envisioned that the channel(s)can be a uniform or non-uniform dimension that travels over some or allof the surface of the reaction chamber inner wall 314 and or surface ofthe nozzle wall 324.

The N₂O that flows along the length of the reaction chamber is typicallyheated from about ambient temperature to about 700° C. Once the N₂Oreaches the reactor cap 310 it is passed into the reaction chamber 302for decomposition. The movement of N₂O over and through the generatorprovides the regenerative cooling of the present invention, as newreactant is constantly flowing through the generator jacket while theheated N₂O is decomposed within the reaction chamber to produce thegas/energy of the device.

As such, and still referring to FIG. 5, N₂O follows the generaldirection of the arrows in the figure, from the injection port (seearrow 338) within the gap, and within the jacket (see arrow 340) to thereactor cap, and ultimately to the reaction chamber (see arrow 342). Gasis released from the reaction chamber in the direction of arrow 344through the exit chamber.

FIG. 6 provides a perspective view of one embodiment of the interiorwall 314 of the reaction chamber 302. In this embodiment, one or morechannels 346 are defined by a series of grooves along the length of theexterior surface of the interior chamber wall 314. The grooves areformed to increase surface area of fluids along the surface of the wall314, but as can be understood by one of skill in the art (and asdiscussed above) other shaped channels can be substituted, e.g.,V-shaped channels, circular-shaped channels, etc. Note that grooves inthis embodiment are direct, but could be zigzagged, spiral or other likeshape. The time N₂O spends within the channel 346 in route to thereaction chamber 302 is important and is dependent on the length of thechannel, the flow rate of the N₂O and the volume of the channels. N₂Othat spends too little time prior to reaching the reactor chamber 302can quench the reactor, i.e., due to the N₂O's insufficient temperature.However, N₂O that heats-up too much in the channels will begin thedecomposition reaction prematurely, leading to high energy gas releasewithin the jacket and thereby leading to generator failure. Therefore,generator embodiments of the invention are designed to coordinate thelength of time the N₂O is heated, i.e., the N₂O's temperature, withinthe channels prior to reaching the reaction chamber. Note the exitzones: convergence, 328, throat 330 and divergence 332.

FIGS. 7 and 8 provide an alternative embodiment of a generator 300 ofthe present invention. In this embodiment, the partition 320 between thereaction chamber 302 and exit chamber 304 is a screen 348 having aseries of internal channels 350 that transversely criss-cross thediameter of the screen. The channels 350 within the screen are designedto force the N₂O entering the generator 300 to come from the entry port326 (see FIG. 8) along the nozzle wall 324 (between the nozzle wall 324and injection cone 308) and then go transversely through the screen 348before re-entering the gap 312 on the other side of the screen. Notethat a flange 352 (see FIG. 8) or other like obstruction prohibits theN₂O from bypassing the screen. The flange 352 radially extends from thescreen to contact the exterior wall 316 or injection cone 308, therebyseparating the channels 354 prior to the screen from the channels 356after the screen.

FIG. 8 illustrates a flow configuration through this embodiment byshowing arrow 356 where the N₂O enters the generator traveling betweenthe nozzle wall and injection cone. Arrow 358 shows the flow of N₂Oacross the screen and up along the channels formed in the interiorchamber wall 324. N₂O is then diverted by the interior of the reactorcap into the reaction chamber. (See arrow 360) As the N₂O decomposes,high energy gas exits the reaction chamber via a series of openings 364in the screen into the exit chamber (See arrow 362). High energy gasultimately exits the generator as shown by arrow 366.

FIG. 9 provides an expanded perspective view of the screen 348 andnozzle of the generator 300 according to an embodiment of the invention.N₂O enters into the transverse channels 350 (see FIG. 7 & FIG. 12) ofthe screen via channel openings 368, exits the screen via channel exits370. This design compels N₂O to move from the injection port side of thescreen itself, through the screen, and into the grooves along thesurface of the reactor chamber wall 324. In general, the transversechannels through the screen connect a first end of the channel on theentry side of the flange 352 to a second end of the channels on the exitside of the flange. As such, the channels cut transversely through thescreen 348 at an angle sufficient to cross the thickness of the flange(See bracket 372).

FIG. 10 is a perspective view of N₂O flowing through a screen 348embodiment of the invention (see arrow 374), N₂O flowing through thescreen is preheated by the escaping gas via openings 364. (See FIG. 8),which serves as a superior heat exchange element, within the screen 348itself. This embodiment can allow for further compaction of thegenerator as N₂O can be preheated in the screen 348. In addition, thecooling provided by the flowing N₂O within the transverse channels 350protects the integrity of the screen. The escaping gas from the reactionchamber places an extreme burden on the integrity of the screen itself,so the regenerative cooling of the screen limits damage and increasesdurability of the screen and therefore the generator. The regenerativecooling aspect of the screen allows for use of metals for screencomponents.

Note that other generator configurations can be used, for example, thegrooves being milled into the exterior chamber wall 316 of the jacket308, and having a smooth outer surface of the interior chamber wall. Themain issue being to provide heat-exchange zones for preheating the N₂Oand cooling the decomposition reaction within the reaction chamber. Notealso that both the interior and exterior chamber walls forming thejacket can be smooth, essentially forming one channel.

FIG. 11 is an illustrative cross-sectional view along line 11-11′ ofFIG. 7. Note the “release” openings 364 in the screen 348 for release ofgas out of the reaction chamber 302. The orientation of the openings canbe of any useful layout as long as there is sufficient capacity torelease the gas from the reaction chamber into the exit chamber 304. Itis also noted that various numbers of openings can be used to accomplishthis feat. Still referring to FIG. 11, grooves defined in the interiorchamber wall 314 of the reaction chamber 302 are shown in the jacket306. Note that the grooves and exterior chamber wall 316 form a seal toensure consistent pressure on the N₂O moving along the chamber towardthe reactor cap. There is no mixing of N₂O between channels in thisdesign. However, it is envisioned that the fluid within the channelscould be mixed with little practical effect on the generator'sperformance.

FIG. 12 shows the juxtaposition of the N₂O release openings 364 versusthe transverse channels 350 through a cooled screen 348 embodiment ofthe invention. Note that other configurations can be used as long asheat transfer/regenerative cooling and generator function aremaintained. There is no set number of transverse channels through thescreen, although 4 to 12 are typical. There is no set number of releaseopenings through the screen, although 9 are typical.

Note that while the previous discussion has centered on generatordesigns using flow in the jacket gap in the direction counter to theglow within the reaction chamber, alternative embodiments are possible,including designs in which the flow in the jacket gap and reactionchamber are in the same direction or coaxial entering the chamberradially from all sides.

Generator Manufacture

Generator embodiments of the invention are typically fabricated fromnickel, steel, or other like metal. Nickel surfaces can further becoated with MgO to provide further resistance to oxidation and damagecaused by the N₂O decomposition.

With regard to catalyst, preferred embodiments include a catalyst bedconstrained within the reaction chamber for facilitating N₂Odecomposition. Catalysts are typically incorporated into the chamber bybeing placed within prior to welding or held in place by a flange orhinge that can be opened repeatedly.

Generator Use

In order for embodiments of the present invention to function as acompact system, the generator is cooled, preferably regenerativelycooled, and the nitrous feed preheated to ignition temperatures beforebeing injected into the catalyst bed. Potential catalysts includerhodium, ruthenium, platinum, nickel, iridium, zirconia, magnesia andcopper, all on appropriate substrates such as alumina, zirconium oxide,or magnesium oxide. If it is not so preheated, the injection of largeamounts of cool nitrous into a relatively small bed will cool the bed tobelow reaction temperatures, quenching the generator. These requirementsare met in principle by using the nitrous feed as a regenerativecoolant, feeding it into the reaction chamber via a jacket around thechamber, as illustrated schematically in FIGS. 3-11. In this way, thefeed nitrous is preheated while simultaneously cooling the generator.

Although not specifically shown herein, other cooling embodiments areenvisioned to be within the scope of the present invention. For example,diluents can be included into the N₂O feed prior to decomposition withinthe reaction chamber. Diluents would essentially “water” the reactiondown so that lower temperatures would be attained during thedecomposition reaction. Diluents of the invention include a N₂O misciblematerial like CO₂ and/or N₂O non-miscible materials like H₂O. So, forexample, CO₂ can be combined with the N₂O prior to addition within thegenerator to “water down” the decomposition reaction to a level requiredfor the particular use. This would thereby lower the maximum temperatureof the generator and increase the durability of the generator due to thedecreased temperature of the gas being produced. With regard to water,the water could be sprayed into the reaction chamber via an entry pointseparate from the N₂O. Water can be moved into the generator via gaspressure or using pumps. Other cooling embodiments include a separatejacket for moving water or other like liquid over the reaction chamberwherein the heater water is discharged from the generator once itattains a predetermined temperature.

In one illustrative embodiment, CO₂ is combined with the nitrous feed.CO₂ and N₂O are miscible, and since CO₂ is inert, its presence lowersthe overall generator system temperature. For example, addition ofapproximately 10% CO₂ to a stream of N₂O will lower the temperature ofreleased gas by about 200° C.

In an alternative embodiment where water is used as an injected coolantthe water is not miscible with N₂O, so that a separate feed system isrequired. However as water does not react with room temperature N₂O, N₂Ogas can be used as a pressurant to drive the water injection. Water canbe used as a coolant by flowing it through cooling channels or sprayingit directly into the reaction chamber.

In use, the generator is started by preheating the reaction chamber to asufficient temperature, about 700° C. is typical. Preheating of thechamber is accomplished by electrical, chemical and other like heatingmeans. In an illustrative manner, heat tape can be wrapped around thegenerator which can be used to electrically preheat the chamber. Inaddition, separate reactors can be included in the generator or separatefrom the generator to provide heat to the N₂O reaction chamber. Theseseparate reactors can accommodate a solid pyrotechnic device (blackpowder, cordite, etc), or a fuel source like gasoline, methane,hydrogen, propane or other reactants that will ignite in combinationwith an oxidizer, such as air, oxygen or N₂O. The energy released fromthese separate reactions is then released into the N₂O reaction chamber(not shown). In addition, a small amount of N₂O dissociation in a smallgenerator can be used to generate hot gas to heat the larger reactionchamber volume of a large generator.

In some uses, a catalyst is added to a bed within the reaction chamberthat can survive the high temperature and oxidizing environment of thegenerator's operation, this will allow the temperature required to causenitrous reaction in the bed to be lower than the temperature needed tocause reaction in the (uncatalyzed) jacket. The difficulty associatedwith this approach is that the catalysts that can survive the reactor'shigh temperature oxidizing environment are not always strong, i.e. notso effective at lowering minimum reaction temperature, and so theoperating margins associated with this approach used alone can benarrow.

In alternative uses, the generator is designed to have a jacket thatminimizes the time that the coolant spends in the jacket (residencetime) so radically that the nitrous does not have time to react beforeit is injected into the bed. The reaction time for nitrous oxide as afunction of temperature in the presence of various catalysts is shown inFIG. 16.

In general, for generator failure to be avoided, the N₂O jacketresidence time must be kept shorter than the N₂O reaction time. Thisgenerator design can be challenging, because the nitrous oxide mustsimultaneously spend enough time in the jacket to warm up. These twoconflicting requirements are reconciled by machining the jacket in suchas way as to maximize its heat transfer area, thereby allowing a greatdeal of nitrous heating to occur within a very short residence time. Inone particular design, a generator is built with a total mass flow of 25gm/s, the jacket interior volume is kept to 2.99 cm³, which limits theresidence time of the fluid in the jacket to less than 3.5 milliseconds.This is much shorter than 50 millisecond reaction time that might beexpected if the fluid in the jacket were to reach 900° C., so exothermicreaction of the fluid in the jacket will not occur. In order to assuresufficient preheating in this design, 40 grooves with a total surfacearea of 75 cm² are milled into the jacket.

For best operation, both of the above embodiments (catalyst and limitedgap residence time) are typically used in combination.

Another challenge addressed to enable durable N₂O generators of theinvention is material compatibility. Hot nitrous, and its dissociationproducts, create an oxidizing environment that can be quite damaging tomost metals. The present invention provides that nickel is fairlyresistant to this environment, enabling the operation of such generatorsfor considerable time before potential failure. Nickel also has theadvantage of being much more thermally conductive than most metals (itis four times as conductive as stainless steel) thereby making it a goodmaterial for use in a regenerative cooled embodiment which must transferheat quickly away from the reaction chamber. In addition, materials canbe used to coat and protect the nickel from the extreme environments ofthe interior of the generator. For example, nickel has a thermalexpansion coefficient which is nearly identical to that of magnesiumoxide (MgO). MgO in turn has a melting point above 3000 K, and is highlyresistant to oxidizing atmospheres to at least 2500 K. The MgO istherefore used, in some embodiments, to coat the nickel and therebyprotect the nickel from the extreme environment within the generator.The MgO also is so tightly bound that it will not react with the nickel,i.e., where MgO is coated on nickel. As such, embodiments of thegenerator include coating parts of the reactor in MgO.

By making use of various combinations of the innovations of nitrousregenerative cooling, high temperature oxidation resistant catalysts,minimum residence time cooling jackets, specially machined highheat-transfer area cooling jackets, nickel construction, and potentiallyinert fluid injection and MgO protective coatings on high temperaturenickel parts, as required, the present invention is enabled.

The generator embodiments of the present invention provide N₂O as ameans of generating large quantities of high energy gas. Generatorembodiments of the invention can be used for numerous applications,including but not limited to: 1) monopropellant rocket engines, 2)bipropellant or hybrid rocket engines, 3) buoyancy engines forunderwater vehicles, 4) monopropellant drivers for turbine emergencypower units (EPUs), 5) sources of breathing gas for individuals,shelters, and land, sea, air and space vehicles; 6) operating pneumaticmachinery; 7) providing heat for use as a sterilizing agent; 8)providing gas for inflating an inflatable structure; and 9) providingheat to a constrained environment. In each of these cases, theembodiments are particularly useful due to the high efficiency of thegenerator and portable sizes of the generator. Several illustrative usesare described below:

Monopropellant Engines

The embodiments of the present invention address both the storabilityand performance requirements of conventional liquid monopropellants.Nitrous oxide, N₂O, is not hazardous even if inhaled in highconcentrations. Anesthetic effects of N₂O can occur if it is breathed invery high (˜65%) concentrations, but no ability-diminishing effects inhumans have ever been observed at concentrations lower than 20%. Thereis no IDLH or OSHA permissible exposure limit (PEL) listed for N₂O. Forcomparison, OSHA recently reduced the PEL for hydrazine from 1 to 0.1parts per million (ppm). Nitrous oxide is very stable at roomtemperature, and will not normally decompose spontaneously; thus, it isstorable for extended periods of time, and is relatively easy to handle.Although its specific impulse is slightly lower (typically, 10 to 15%lower specific impulse performance) than that of hydrazine, these otheroperational considerations more than compensate, making nitrous oxide anattractive alternative to hydrazine for nearly all monopropellantapplications.

In addition, since the decomposed reaction products of N₂O contain aconsiderable amount of unreacted O₂, a hydrocarbon fuel can beintroduced downstream of the decomposition reactor (preventing carbonfouling of the reactor bed) to boost I_(sp) performance of the generatorsystem to approximately 300 s. An engine configuration that maintainsmonopropellant-like plumbing and operational characteristics would be ahybrid engine, where the hot generator exhaust products are run througha solid hydrocarbon fuel grain (for example HTPB or polyethyleneplastic) before exiting through a nozzle (the nozzle having theconfiguration as described above). In such a configuration, one wouldhave bipropellant performance with the stability and safety handlingcharacteristics of pure N₂O.

In terms of potential integration with an EVA system, the decompositionproducts of N₂O provide an O₂ enriched air (33% O₂-67% N₂ vs. standardatmospheric air of 20% O₂ in a nitrogen-rich buffer gas) with propermanagement of NO_(x) production. Based on similar O₂ partial pressures,a generator of the present invention could be run down to about 9 psiawithout O₂ enrichment.

Conventional liquid monopropellants are used in propulsion systems wheresimplicity of design, control on demand, and repeatability are desired.However, many monopropellants, such as hydrazine and hydrogen peroxide,are toxic and dangerous, adding to the complexity and cost of theirutilization for satellite RCS systems and ruling them out completely forspacesuit thruster (EMU) application.

Liquid monopropellant engines, by their nature, have very simplepropellant feed systems. The lack of multiple propellant feed systemsand propellant-mixing requirements typically leads to very simpledesigns. Currently, monopropellant based engines are used extensively inpropulsion systems where simplicity and small repeatable thrust impulsebits are required, such as in reaction control systems on spacecraft.

The most commonly used liquid monopropellant is hydrazine. Hydrazine isfairly stable in liquid form, and thus is relatively storable. It alsohas relatively good specific impulse for a liquid monopropellant. It iscommonly used in attitude control systems of spacecraft, as previouslymentioned. Unfortunately, hydrazine is extremely toxic to humans, and ishazardous to breathe or touch. Its toxicity makes it difficult, and thusexpensive, to handle. Time consuming, complex, costly procedures must beused to fuel (ground process) rocket engines that use conventionalhydrazine propulsion systems. These procedures have become so onerous,in fact, that they are materially adding to the cost and complexity ofAtlas Centaur launch operations. (The Centaur uses hydrazine thrustersfor tank settling during its long LEO-GEO coast). For EVA mobilityapplications, hydrazine is out of the question, since the exhaust plumewould contaminate the astronaut's spacesuit and a tank leak duringstorage would endanger the entire spacecraft crew.

Hydrazine is also used as a monopropellant to drive some aircraftemergency power units (EPUs) such as that employed on the F-16. Itstoxicity has caused many operational, safety, environmental, andregulatory problems in that application as well, so much so that theUSAF has declared it a priority to eliminate hydrazine from the flightline.

Hydrogen peroxide was used in some simple liquid rocket systems. Decadesago, hydrogen peroxide was used in the rocket propulsion systems of somerocket-powered aircraft and as a gas generator propellant.Unfortunately, it has a relatively low specific impulse. Additionally,hydrogen peroxide is itself somewhat toxic and has a tendency tospontaneously decompose, making it difficult to handle safely andcreating potential accident scenarios that could lead to the loss of theentire craft. Thus, hydrogen peroxide has limited use in modernmonopropellant engine systems. For EVA applications hydrogen peroxide ispatently unacceptable because the water vapor in the exhaust could frostout on helmet visors, leading to loss of vision for an astronaut.

In one embodiment of the invention, therefore, a N₂O generator of theinvention generates high energy gas from nitrous oxide, a readilyavailable safe and storable propellant that is non-toxic, havingperformance comparable to hydrazine, and does not decomposespontaneously like hydrogen peroxide. The embodiment provides the use ofthe generator as a monopropellant engine, for example as a rocketengine. Incorporation of generator embodiments of the invention intorockets or other like vehicles would be known in the art, analogous toincorporation of conventional rocket engine features into a rocket.

Breathable Gas

In another embodiment of the invention, the decomposed N₂O is convertedinto a breathable mix of oxygen and nitrogen. This particular use can bepart of a mixed use, for example, using the generator for propulsion andfor, when necessary, production of breathable gas. Thus, for example, anEMU propelled by a generator of the invention would provide an astronautwith a large emergency backup supply of oxygen. Such a dual or mixed usedevice has great utility as the propulsion system for manned spacecraft,such as the International Space Station, Space Shuttle, or CrewExploration Vehicle, where safety is paramount and breathing gasreserves are desired. Breathable gas production is based on thegenerator of the present invention using modifications as described inU.S. Pat. No. 6,347,627 which is incorporated by reference in itsentirety. Combination uses are termed “mixed uses” herein and caninclude a combined use of the N₂O generator, noting the efficiency ofbeing able to use one source of material (N₂O) for multiple purposes.

It is demonstrated herein, therefore, means of dissociating nitrousoxide into nitrogen and oxygen. (2N₂O═>2N₂+O₂) (see U.S. Pat. No.6,347,627 B1. In embodiments of the invention, the generator of thepresent invention improves upon this work by providing a much morecompact and lightweight generator for driving such a nitrous oxide basedoxygen supply system. In alternative embodiments of the invention, suchas underwater, aircraft, or spacecraft, the generator can serve two oreven three or more functions, including propulsion, power, and breathinggas, with all services drawing their supply from a common resource.

Emergency Power Units

Another embodiment of the invention is used to generate high energy gasto drive an aircraft emergency power unit. Currently there are over 3000F-16's in service around the world, which use hydrazine decompositiongas generators to drive their emergency power units. However because ofthe extreme toxicity of hydrazine, which complicates operations throughboth risk to personnel and the need to comply with increasinglystringent safety and environmental regulations, the USAF has madedecision to eliminate hydrazine from the flightline. Embodiments of thisinvention replace the hydrazine gas generator with a non-toxicalternative, the N₂O based gas generator. Embodiments of the generatorcan be positioned as an emergency power unit which would be ignited incase of an emergency. In such embodiments, a pyrotechnic ignition mayprovide the most effective manner of igniting the nitrous oxidedecomposition reaction. One illustrative embodiment would include agenerator of the invention in an airplane where the generator would beignited and used in case of an emergency engine shutdown. The generatorwould be small and have the capacity to use a small amount of N₂O, sowould be easily integrated into most airplane designs.

Buoyancy Engine

In another embodiment of the invention, the N₂O reactor is a buoyancyengine for underwater vehicles. The US Navy has a great interest inachieving silent underwater travel. One way to accomplish this is byrepeatedly changing the buoyancy of an underwater glider, allowing it toglide up and down many times, thereby traveling long distances withoutthe use of a propeller. The generator of the invention produces thebuoyancy gas required for such a vehicle from a liquid storagereservoir, and its potential for producing high temperature gas adds toits efficiency by allowing a given mass of gas to displace a larger massof water than would be possible using room-temperature buoyancy gas.Note that gas expelled from the generator of the present invention isused to blow ballast tanks. For example, in one test conducted atPioneer Astronautics, 540 gm of N₂O was used to produce hot gas withwhich to blow a 30 liter tank against a back pressure of 500 psi. Thispressure is equivalent to that at 1122 ft (342 m) under the sea. The 540gm of N₂O, stored at 20° C. could be contained within a 0.8 liter bottlewith a rated pressure of 700 psi. In contrast, if compressed air wereused to accomplish the same blowdown task, a 5 liter tank with a ratedpressure of 3000 psi would have been required to store the required gas.The N₂O system can thus provide the required gas for buoyancy changeusing a tank of 116^(th) the volume, 114^(th) the pressure, and1124^(th) the mass of that needed by a system employing compressed air.

Hybrid Engine

Decomposition reaction products of N₂O contain a considerable amount ofun-reacted O₂. As a result, introduction of a hydrocarbon fuel sourcedownstream of the decomposition reaction can be used to boost Isp (forexample to 300 s). As such, embodiments of the present invention includeadding hydrocarbon fuel into the gas exhaust of the generatorembodiments of the present invention. In preferred embodiments,hydrocarbon is added to a generator exhaust to boost performance bypositioning either a solid hybrid fuel grain or a liquid fuel injectionsystem downstream of the generator.

The following examples are provided for illustrative purposes only andare not intended to limit the scope of the invention.

EXAMPLES Example 1 Nitrous Oxide is Comparable to Hydrazine in StorageCharacteristics

FIG. 13 illustrates the vapor pressure and density curve for nitrousoxide (N₂O) as a function of temperature. The curve shows that N₂Oprovides comparable thermal control to hydrazine: (1)—23° C., N₂O hasthe same density as hydrazine (1.01 g/cc); (2) N₂O has a heat ofvaporization of 376 kJ/kg, therefore, starting at a worst case of 25°C., 10% of the N₂O could be vented to bring the residual N₂O down to−23° C., and (3) large insulated N₂O tanks can be maintained athydrazine storage densities by pressure relief boil-off (similar to theprocess in cryogen tanks) to get up to about 30% gain in storagedensity, the process could continue indefinitely to a worst-caseself-regulating storage density of about 0.7 g/cc at 25° C.

Alternatively, N₂O can be stored at room temperature, giving it adensity, at 20° C., greatly exceeding that of cold gas. In addition, forexample, unlike hydrazine which requires special loading operations forEVA propulsion, N₂O provides safe and convenient ground loading, evenallowing for last minute N₂O loading just prior to launch.

The present example shows the utility of replacing hydrazine with N₂O inapplications conventionally performed by hydrazine.

Example 2 Nitrous Oxide Decomposition as a Function of AdiabaticTemperature and Maximum Theoretical Isp

FIG. 14 illustrates adiabatic temperature and maximum theoretical Ispperformance from decomposed liquid nitrous oxide (LN₂O) as a function ofpercent decomposition and initial tank temperature. The enthalpy ofreaction for N₂O is 1855 kJ/kg; including the heat of vaporization loss(376 kJ/kg), the resultant available thermal energy release from LN₂O is1479 kJ/kg (410 Whr/kg). As such, 20% of the decomposition energy isrequired to vaporize the liquid nitrous oxide. Note that the meltingpoint boundaries of the nickel and stainless steel are included in thegraph for comparison.

The present example shows the utility of using nitrous oxide as amonopropellant.

Example 3 Increased Temperature Improves Decomposition of N₂O

FIG. 15 illustrates the improvement in N₂O decomposition as a functionof increasing temperature. FIG. 15 shows the sensitivity ofdecomposition time as a function of temperature for the two boundingcases of isothermal flow and more realistically, isenthalpic flow(decomposition times of milliseconds tend to not provide enough time toeffectively transfer heat out of the flow). Thermal decomposition,therefore, appears to take off in the vicinity of 900° C. to 1,000° C.(elementary reactions for LN₂O decomposition were collected and run inCHEMKIN (Sandia National Laboratories, 1996).

The thermal decomposition times for N₂O versus its initial gastemperature shows that every 100° C. increase in temperature results inabout 1 order of magnitude improvement in decomposition time. Therefore,the biggest improvement in decomposition times is associated withincreasing the temperature of the incoming N₂O prior to it hitting thereactor bed.

Other ways to improve N₂O decomposition are generally associated withaddition of catalyst.

The present example shows the utility of pre-heating the N₂O prior toits entry into where it decomposes, i.e., reactor bed.

Example 4 Residence Time of N₂O Must be Less than Reaction Time

FIG. 16 illustrates reaction time for N₂O as a function of temperaturein the presence of various catalysts. The residence time of N₂O in areactor device of the present invention (i.e., in the reactor's jacket)must be kept shorter than nitrous oxide's reaction time (i.e., in thereactor's reaction chamber). Conversely, as discussed above, the nitrousoxide must simultaneously spend enough time in the reactor device'sjacket to warm-up in accordance with the preceding. The two conflictingrequirements (N₂O warm-up but not react) in the reactor's jacket arereconciled in embodiments of the devices described herein. For example,the jacket can be designed to maximize the heat transfer area of thereactor to allow greater N₂O heating to occur within a very shortresidence time.

For example, with a total mass flow of 25 g/s, the reactor jacketinterior volume is kept to 2.99 cm³, which limits residence time of thegasified N₂O to less than 3.5 milliseconds. This amount of time isshorter than the 50 milliseconds, i.e., the time required for the N₂O toreach 900° C. As such, in one embodiment, the reactor jacket is designedto incorporate 40 grooves with a total surface area of 75 cm².

The present example illustrates the utility of providing a reactorjacket designed to increase the N₂O temperatures without allowingdecomposition in the jacket, but that allows decomposition in thereactor bed to proceed more efficiently.

Example 5 Magnesium Oxide and Nickel are Useful Fabrication of N₂OReactors of the Present Invention

Hot N₂O (and its dissociation products) creates an oxidizing environmentharmful to the stability of most metals. The inventors have found thatnickel is a resistant metal to the environment, i.e., slow to oxidize.Nickel has the added advantage of being thermally conductive (4 times asconductive as stainless steel), thereby making it a good material foruse in fabricating reactor devices of the present invention. Therefore,nickel provides the dual benefit of withstanding N₂O but being able toconduct heat through the reactor jacket, as discussed in Example 4.

In addition, nickel has a thermal expansion coefficient nearly identicalto magnesium oxide (MgO). MgO coatings on nickel can therefore bedurable under conditions of thermal cycling. Magnesium oxide, in turn,has a melting point above 3000 K and was tested by the present inventorsto be highly resistant to oxidation to at least 2500 K.

The present example shows the utility of fabricating parts of the N₂Oreactor of the invention from nickel. Further, these nickel parts can becoated with MgO to provide addition protection from oxidation during N₂Ouse.

Example 6 Isp of N₂O is Comparable to Hydrazine and H₂O₂

The specific impulses of hydrazine, N₂O, and 98% hydrogen peroxide arecompared in Table 1. These theoretical specific impulse data wereobtained from the Phillips Laboratory AFALS equilibrium chemistry rocketspecific impulse code, using a chamber pressure, P_(c), of 100 psia andan expansion ratio, 8 of 50. As shown in Table 1, nitrous oxide has thepotential to provide specific impulse (Isp) performance that iscomparable to current industry standard monopropellants such ashydrazine and hydrogen peroxide.

TABLE 1 Comparison of Candidate Monopropellants (P_(c) = 100 psia, ε =50). Chemical Isp Monopropellant Formula (s) Hydrazine N₂H₄ 220 98%Hydrogen Peroxide H₂O₂ 180 Nitrous Oxide N₂O 196

Any of the liquid monopropellants listed in Table 1 would offer greatlyimproved performance over the cold compressed gaseous nitrogen systemused for propulsion on some satellites and current EMU systems. Incontrast to these liquid monopropellants, the current cold nitrogen gassystem offers a specific impulse of only 70 seconds, and offers apropellant mass fraction (defined as the mass of propellant divided bythe mass of the tank required to hold it) that is about a factor of 20worse. However the conventional monopropellants listed above, hydrazineand hydrogen peroxide, both have safety problems that have ruled themout for EVA propulsion application.

Example 7 Generator Embodiments are Effective at Blowing Ballast Tanksfor Underwater Applications

Generators can be advantageously used to blow ballast tanks ofunderwater vehicles. For example, in one test conducted by theinventors, 540 gm of N₂O was used to produce hot gas which to blow a 30liter tank against a back pressure of 500 psi. The production of therequired gas by the generator was accomplished in about ten seconds. Thesystem pressure was equivalent to that at 1122 ft (342 m) under the sea.The 540 gm of N₂O, stored at 20 C could be contained within a 0.8 literbottle with a rated pressure of 700 psi. In contrast, if compressed airwere used to accomplish the same blowdown task, a 5 liter tank with arated pressure of 3000 psi would have been required to store therequired gas. The N₂O system can thus provide the required gas forbuoyancy change using a tank of 116^(th) the volume, 114^(th) thepressure, and 1124^(th) the mass of that needed by a system employingcompressed air.

It will be clear that the invention is well adapted to attain the endsand advantages mentioned as well as those inherent herein. While anumber of embodiments have been described for purposes of thisdisclosure, various changes and modifications can be made which are wellwithin the scope of the invention. Numerous other changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are encompassed in the spirit of the invention disclosure hereinand as defined in the appended claims. All publications cited herein areincorporated by reference.

1. A system for nitrous oxide decomposition comprising: nitrous oxide,and a gas generator comprising: a reaction chamber for accepting nitrousoxide at a first port and for releasing gas from the nitrous oxidedecomposition at a second port, the reaction chamber having an interiorand an exterior chamber wall, the interior chamber wall for constrainingthe nitrous oxide decomposition reaction and the exterior chamber walldefining a jacket between it and the interior chamber wall; and thejacket at least partially enveloping the reaction chamber, the jacketdefining one or more channels between the interior chamber wall and theexterior chamber wall, the one or more channels for transporting thenitrous oxide within the jacket from the first port of the reactionchamber and for facilitating the transfer of heat generated during thenitrous oxide decomposition to an incoming source of nitrous oxide, theincoming source of nitrous oxide being preheated to more efficientlydecompose within the gas generator, and wherein the reaction chamber isregeneratively cooled by the incoming nitrous oxide.
 2. The system ofclaim 1, wherein the residence time of the nitrous oxide in the jacketis shorter than the reaction time of nitrous oxide in the jacket.
 3. Thesystem of claim 1, wherein the reaction further comprises a catalyst toreduce the temperature required for the nitrous oxide decomposition. 4.The system of claim 3 wherein the catalyst is selected from the groupconsisting of rhodium, ruthenium, platinum, copper, iridium, nickel,magnesium oxide and zirconium oxide.
 5. The system of claim 1 wherein atleast a portion of the gas generator used to constrain the nitrous oxidedecomposition is constructed from nickel.
 6. The system of claim 5wherein the nickel is coated with MgO.
 7. The system of claim 1, whereinthe reaction chamber volume is from about 0.5 cubic inches to about 12cubic inches.
 8. The system of claim 1 wherein the gas generatordissociates nitrous oxide into breathable nitrogen and oxygen.
 9. Thesystem of claim 1 wherein the gas generator is part of a monopropellantrocket engine system.
 10. The system of claim 1 wherein the gasgenerator is part of a hybrid engine system combining nitrous oxidizerwith a solid fuel source.
 11. The system of claim 1 wherein the gasgenerator is part of a power generating system.
 12. The system of claim1 wherein the gas generator is a buoyancy engine for underwatervehicles.
 13. The system of claim 1 wherein the gas generator is usedfor dissociating nitrous oxide into nitrogen and oxygen for use as asterilizing agent.
 14. The system of claim 1 wherein the gas generatoris part of a pneumatic machine.
 15. The system of claim 1 wherein thegas generator is used for dissociating nitrous oxide into nitrogen andoxygen for inflating an inflatable structure.
 16. The system of claim 1wherein the gas generator is used for dissociating nitrous oxide intonitrogen and oxygen for use in providing heat to a constrainedenvironment.
 17. The system of claim 1, wherein the gas generatorfurther comprises a gap in the jacket, the gap providing a constrainedspace by which nitrous oxide flows into the reaction chamber.
 18. Amethod for nitrous oxide decomposition comprising: providing a gasgenerator comprising a reaction chamber, the reaction chamber having aninterior and an exterior chamber wall, the interior chamber wall forconstraining the nitrous oxide decomposition reaction and the exteriorchamber wall defining a jacket between it and the interior chamber wall,the jacket at least partially enveloping the reaction chamber anddefining one or more channels between the interior chamber wall and theexterior chamber wall, the one or more channels for transporting thenitrous oxide within the jacket into the reaction chamber; pre-heatingincoming nitrous oxide in the jacket to a temperature of at least about600° C. while minimizing the residence time of the nitrous oxide in thejacket, wherein the temperature and residence time of the nitrous oxidewithin the jacket facilitates cooling of the interior chamber wall;transporting nitrous oxide within the jacket into the reaction chamber,wherein the temperature and residence time of the nitrous oxide withinthe reaction chamber facilitates nitrous oxide decomposition; andreleasing gas from the nitrous oxide decomposition from the reactionchamber.
 19. The method of claim 18, wherein the gas generator furthercomprises a catalyst constrained within the reaction chamber.
 20. Themethod of claim 19, wherein the catalyst constrained within the reactionchamber is selected from the group consisting of rhodium, ruthenium,platinum, magnesium oxide and zirconium oxide.
 21. The method of claim18, wherein the reaction chamber further comprises a screen forconstraining a catalyst within the reaction chamber.
 22. The method ofclaim 21, wherein the screen is composed of zirconia or sodium zirconiumphosphate.
 23. The method of claim 21 wherein the screen has one or morechannels therethrough, the channels through the screen fluidly connectedto the one or more channels formed in the jacket wherein the channelsthrough the screen contribute to cooling of the screen.
 24. The methodof claim 18, wherein the one or more channels are grooves formed in thesurface of the interior chamber wall.
 25. The method of claim 18 whereinthe one or more channels are grooves formed in the surface of theexterior chamber wall.
 26. The method of claim 18, wherein the gasgenerator further comprises a nozzle operatively connected to thereaction chamber for control of the gas release from the reactionchamber.
 27. The method of claim 26, wherein the nozzle has aconvergence zone, a throat and a divergence zone wherein the convergencezone concentrates the gas flow, the throat controls the gas flow rateand the divergence zone accelerates the velocity of the gas releasedfrom the nozzle throat.
 28. The system of claim 1, wherein the generatoris heated to an initial operating temperature electrically.
 29. Thesystem of claim 1, wherein the generator is heated to an initialoperating temperature by hot gases produced by chemical combustion. 30.The system of claim 1, wherein the generator is heated to an initialoperating temperature by hot gas produced by a smaller generator. 31.The system of claim 1, wherein the volume of the reaction chamber is atleast an order of magnitude larger than the total volume of the one ormore channels in the jacket.